imagescnan.m v2.1 (Aug 2009)

Same as IMAGESC but ignores NaNs.

Description

Syntax:
>> imagescnan(Z) % Uncolored NaNs
>> imagescnan(Z,'k') % Colored

IMAGESC is a good option when the user doesn't like the interpolating behaviour of SURF or PCOLOR, because EVERY element is drawn as a single pixel CENTERED with the axis value.

The problem with this function is that it doesn't work properly with NaNs elements (although sometimes SURF neither does): they are drawn with the lower color of the current colormap.

This functions uses IMAGESC but ignores the NaNs elements.

The user can specify the NaNs color, a different color mask, or another value to be ignored.

If the user gives X and Y data with no constant increment, PATCH is used instead of IMAGESC (this is experimental!).

To freeze the colormap check COLORFREEZE and CBFREEZE here at the FileExchange.

(Bugs reports and suggestions will be very appreciated)

Acknowledgements

Image Overlay, Spyx.M, Ndnanfilter.M, and Freeze Colors / Unfreeze Colors inspired this file.

This file inspired Colormap And Colorbar Utilities (Sep 2009).

• MATLAB release: MATLAB 7.7 (R2008b)

[Ste]

 

[Nicolas Beuchat]

Excellent function, I had a little function that put the NaN white but this one is much more flexible! Thanks!

[Mario Trevino]

gracias!

[Felipe G. Nievinski]

why not do simply:
imagesc(img, 'AlphaData',~isnan(img))
where, e.g.,
img = membrane(1,25);
img(1:10:end) = NaN;

[Kaushik]

Hi, thanks a lot this was very helpful. However, as Camille has pointed out, the axis lebels appear mirrored at times. This doesnt happen all the time, but mostly at times when there are too many NaNs in the Matrix. Is there a workaround?

[Camille Couzi]

Hi again, I am having the same problem as Yu-nung Nina in 2009:
"Axis labels of both axes flip (the numbers become "mirror image" of normal axis tick labels) "
Please can you write here what solution you found to that problem?
Thanks a lot
Camille.

[Camille Couzi]

Millones de gracias por esta herramienta super util y facil de usar!!!!

[Cesare]

 

[Carlos Adrian Vargas Aguilera]

Yes Olivier, or with:
>> imagesc(U,'AlphaData',~isnan(U),'AlphaDataMapping','none')
I just wanted to be able to paint NaNs with specifyc color without modifying the axes color.
Probably I should include this "transparent" option. Thank you!

Carlos

[Olivier Ripoll]

another way to obtain this is simply (fo a given array M):

alpha(imagesc(M),double(~isnan(M)))

You can of course get all the imagesc options since you can it directly.

[Ben]

 

[David Wang]

Anyway, that won't make life easier. Probably I should simply do this:

pcolor((x(1:end-1)+x(2:end))/2, (y(1:end-1)+y(2:end))/2, c(2:end,2:end));

It's not perfect. The first/last column/row get dropped. But it should be sufficient for my use...

[David Wang]

Thanks for your response, Saludos.

First, PCOLOR(X,Y,C) regards X,Y as the edges of pixels, while IMAGESC(X,Y,C) regards X,Y as the centers of pixels. The latter is what I need.

Second, what I want is not 'interp' but 'faceted', namely facet lines at the edges of pixels, which is what PCOLOR does by default:
http://www.mathworks.com/access/helpdesk/help/techdoc/ref/pcolor1.gif

D.

[Carlos Adrian Vargas Aguilera]

Yes (kind of) but first, why would you like to do so if you can do it with PCOLOR? Well...

% Change line 359:
if aequal
%by:
if 0

% On empty line 398 write:
U = [U U(:,end); U(end,:) U(end,end)];
% Which is the trick. You may try other ways.

% Finally, change line 404:
'FaceColor','flat',...
% by:
'FaceColor','interp',...

% And that is it. Try imagescnan(peaks(5)) and you'll see the problem, which is that the interpolation is done on the edges and not on the middle of the faces (sort of). Maybe some day...

Saludos, Carlos Vargas

[David Wang]

This is a great script. I've got a relevant question. Do you know if it is possible to make imagesc/imagescnan draw facet lines as shading facets applies to pcolor?

Thanks!

[Carlos Adrian Vargas Aguilera]

I guess not Yu-nung, the program may flip the image if your axes are decreasing, but never the ticks. Try a normal IMAGESC or send me your script. Carlos

[Yu-nung Nina]

One small mistake in my comment: on my personal laptop, the plot looks normal WITHOUT these two bizard things happening.

[Yu-nung Nina]

Hi, this script is fantastic. However, I found 2 strange things happen:

1. Axis labels of both axes flip (the numbers become "mirror image" of normal axis tick labels)
2. When I try to plot a matrix of size 420x810, the plot does not complete itself. Instead the script only plots the first few rows and stops.

These two things happen on my lab computer (with matlab R2006a, R2008a, R2008b on it; I tried all of them). But on my personal laptop, the plot looks normal with these two bizard things happening. Is there any special settings in your code that is related to the computer itself?

[Gus Silva]

This problem has been bothering me for a very long time. Thanks allot!!!

[Carlos Adrian Vargas Aguilera]

Thank you very much Greg!, I already sent and updated file, which also accepts RGB images.

Cheers, Carlos

[Greg King]

imagescnan did just what I wanted (i.e., color NaNs white). However, exploring the color option I found a bug. The doc says that "color" can be a 3 element vector or a character ('k', 'w', etc). In fact only the latter option works. The 3 element color vector results in an error.

[Carlos Adrian Vargas Aguilera]

I submited an updated file that freezes correctly the colorbar.

Carlos Vargas